Delirium is an etiologically nonspecific organic cerebral syndrome characterized by concurrent disturbances of consciousness and attention, perception, thinking, memory, psychomotor behavior, emotion, and the sleep-wake schedule. Different studies suggest that a proper lighting environment for delirium reduction requires a circadian cycle of bright and dark periods that somewhat mimics the natural day and night cycle (Wilson, L. M.: “Intensive care delirium. The effect of outside deprivation in a windowless unit”, Arch Intern Med, 1972, 130, 225-226; Guo, X., Kuzumi, E., Charman, S. C., and Vuylsteke, A.: “Perioperative melatonin secretion in patients undergoing coronary artery bypass grafting”, Anesth Analg, Anaesthetic Research Unit, Papworth Hospital, Cambridge, UK., 2002, 94, 1085-91).